Cooling and supporting structure



y 7, 1959 E. A. RICHARDSON 2,893,703

COOLING AND SUPPORTING STRUCTURE Original Fil ed Dec. 12, 1947 Fig.1Fig.2

Inven'l'or EDWARD ADAMS RICHARDSON Ai'i'arn ya United States Patent C18, 1956. Divided-and this'applicafion-September, 1956, Serial No.611,048

4 Claims. (Cl. 257-450) This invention relates to a cooling andsupporting structure. More particularly it rclatestoa method andapparatus for the transfer of heat involvingthe use of material which ispermeable to-fluids.

The problem of reducing and controlling the temperature of certainstructural parts such'as bearings, cylinder walls, valves and gasturbine blades is constantly under attack. With the rapid increase inthe use of gas turbines, jet and other types of engines involving theoccurrence of very high temperatures, the-need for greatly improvedmeans of reducing the temperature of such structural parts has becomeimperative due to the effective temperature limits ofknown'lubricantsand the inability of many metals and alloys thereof to performsatisfactorily under the high temperatures required.

It is, therefore, an object of this inventionto'provide a method andapparatus whereby achievements of chicient cooling andtemperaturecontrol of material parts subjected to heat and in particularhigh heat is possible.

An additional object of this invention is to provide means for coolingstructural parts which are subjected to heavy loads.

These and other objects will become apparent from the description.

Briefly the present invention involves the use of fluid permeablematerials having good thermal conductivity in conjunction with a fluid.The permeable materials act to conduct heat from a hot structural part,to transfer the heat to a cooling fluid and in some measure also to acolder surrounding structure; It is'generally applicable to thecontrolled cooling of structural parts which support a heavy load sincethe permeable material is such that it can contribute to the overallstructural strength.

An important aspect of the invention is the-use of permeable bodieshaving large surface areas per unit of volume or mass which the fluidused may contact combined with a relatively low permeability. Such abody I is readily formed by the use of fine meshpartiolesand closelyapproaches the desideratum of havingall of the fluid being insubstantial contact with the solid; the distances for heat flow beingmade extremely short through the thinness of the individual fluidstreamspassing throughthe permeable body.

Whereas most heat exchangers depend upon turbulent flow in which thepressure drop increases nearly as the square of the mass rate of flow,the use of permeable bodies results in a fluid flow which issubstantiallylaminar so that the pressure drop is substantiallyas thefirst power of. the fluidmass. flowing. In. general, less power isrequired 'for'securing the transfer of heat becauseof this law, whilethe characteristiccurve ofpower required is more favorable foroperation. and control.

It will be apparent that widevariations of permeabilities will be usedin the embodiments ,of'this invention due to having to compromise attimes with/other factors such as relative uniformity and rate of flow,strength of material, the ability to pick up heat from; another body,

and the object to be attained. Generally. speaking, permeabilityismeasured in terms of the number of cubic feet of air of an assignedinitial temperature such as F. flowing in one hour through eachsuperficial square foot of surface when the pressure drop of the airiso'ne foot. of water pressure per foot of permeable body thickness.Such permeabilities may be at least as great as 14 for heat transferdevices to as. low as, or even much lower than 0.006 for suchfabrications as gas turbine blades.

Where a permeable body is used for maintaining one temperature on a coldsurface and another temperature on a hot surface,- the following formulais characteristic:

H- is the thickness of the permeable material;

Th is the hot surface temperature;

Tc is the cold surface temperature;

K is the conductivity of the solid and contained fluid.

In general the solid free of fluid, and the fluid alone as thoughstationary, are considered to conduct in parallel in determining K atany point.

T is any inner temperature at a distance x from the cold surface;

Ti is the temperature of the. entering fluid;

Cp is the thermal capacity of the entering fluid.

This formula assumes anot too high rate of flow and a permeabilitysuchthat the difference of temperature, at the distance x, between solid andfluid is of the order of a small'fraction of a degree Fahrenheit.

In the design of a particular cooling structure, other factors must beconsidered. The required strength of the structure, the availablepumping pressure, the available space and other factors depending on thespecific problem are all involved.

Fluid permeable bodies of non metallic substances suitablefor use Withinthe scope of this invention are well known'in the art. Examples arebodies formed by bonding variously particles of graphite, carboiundum orquartz. Although developed comparatively recently, the manufacture ofpermeable metal bodies suitable for use in this invention is. equallywell known. Such bodies are usedparticularly in the production offilters and clutch plates.

In the production of filters a sintered powdered compact. of bronze iscommonly used. With a bronze compact, compressive strengths up to 16,000pounds per square inch may be obtained. A wide range ofpermeabilitie'smay be obtained by control of the mesh size of the metalparticles. Since temperature as high as about: 350 F. in an oxygenatmosphere and 900 F. in an atmosphere without oxygen may be applied tocopper alloys without progressive building up of oxide and destructionof the permeable bodies, it will be apparent that permeable bodies suchas those used in the filter art are well adapted to being used in thisinvention.

Variously by the use of different alloys, mixtures of principal alloyparticles and bonding alloy particles such as copper, heat treatment andgreater compaction pressures other even stronger permeable structureshave been obtained. Thus an 0.87 percent carbon iron powder and copperbond powder has been pressed, sintered, repressed and-resintered to givea body having a compressive strength, of 85,000 pounds per square inch.Heat treating this compact results in a compressive strength of 150,000pounds per square inch.

1 metal bonding and surface protection.

deposition is possible.

other purposes such as producing a chemically, resistant Infiltrantalloys in sintered ample, aluminum bronze with a relatively high meltingpoint, high resistance to oxidation up to about 1000 Fahrenheit, andhigh strength, Everdur, beryllium-copascsyos I a.

compacts maybe, for excoin and sterling silver as well as gold alloysare valuable where chemical action must be resisted up tqperhaps as highas 400 to 600 Fahrenheit. Titanium hydride has been used in compacts tosecure a protective alloy surface on the base powder used in thecompact.

These are but a few of the materials readily available for The controlof permeability is secured largely through particle size control and toa less extent through compaction under pressure and the degree ofheating during sintering. Final control may be had by passing weaksolutions, having a slight solvent action on the compact material,through said compacts to secure the desired permeability within closelimits, when the sintered permeability is on the low side. Similarly aweak solution able to deposit metal or non-metallic filler, or colloidalbody in the pores may be used to bring the permeability down from toohigh values. Chemical or electrolytic Such methods may be used for plateor the establishment of a catalytic material in the pores of thepermeable body.

Reference may be made to the following for additional information onfluid permeable materials: a

Design of Powdered Metal Parts, by W. H.-Arata in Product Engineering,vol. XV, No. 8, August 1944, published by McGraw-Hill PublishingCompany; Inc., 330 W. 42nd Street, New York 18, N.Y. 1

Improved Engineering Properties of Parts Made from 7 Iron Powders, byClaus G. Goetzel in Product Engineering, Vol. 18, No. 8, August 1947,published by Mc- Graw-Hill Publishing Company, Inc., 330 W. 42nd Street,New York 18, N.Y.

Powder Metallurgy, a Symposium, edited by John Wulff, published by TheAmerican Society for Metals, Cleveland, Ohio, 1942.

Other forms of permeable material may be utilized equally Well in manyapplications of the invention provided the permeability is relativelylow, the heat conductivity is good and the surface of elements per unitof volume is relatively large. Bodies formed of wire-like or needle-likeparticles with their axes substantially parallel to each other and tothe heat flow and normal to the direction of fluid flow may be used inheat exchangers. In some cases it is practical to use sheet elementshaving permeability secured by scratching one side of each sheet so thatthe scratches of one sheet and the relatively smooth surface of anadjacent sheet shall produce the necessary fine passages on bonding thesheets.

In general, all bodies used should have reasonably high inherentstrength.

It will be apparent that there exists a wide selection of knownmaterials which may be used in this invention.

The qualities of strength, ability to stand up under high heat,permeability and heat conductivity may obviously be combined in aninfinite number of combinations de pending on the characteristicsrequired.

A wide range of fluids may be used in connection with the permeablematerial. Air and other gases, air or other gas carrying a fog of liquidparticles in suspension such as water droplets and water are examples.In most cases the fluids should be properly cleaned so as not to clogthe pores through deposition of suspended solids, precipitants or thelike. Where fluids may generate solid crack- ,-J willbe non-corrosiveandwill not dissolve the permeable material.

For some purposes, a gas such as air into which a heavy fog of liquidparticles has been introduced will have valuable properties in respectto average density and more particularly heat capacity involving thereinthe heat absorption on evaporation of the liquid drops.

In the drawings:

Figure 1 is a vertical cross section of a portion of a bearing and itssupporting members;

Figure 2 is a section taken on a plane indicated at 22 in Figure 1; i I

Figure 3 is a longitudinal vertical section of a ring oiler pillow blockcarrying a shaft;

Figure 4 is a. section taken on a, plane indicated at 4-4 in Figure 3.

In Figures 1 and 2 a bearing 1 is supported by a member 2 which in turnis supported by a member 3. The member 2 is constructed of a fluidpermeable metal having good thermal conductivity and has transversegrooves 4 in its inner face and transverse grooves 5 in its outer face.

A pump 9 through pipe 8 supplies a cool fluid, for example, air, underpressure to a chamber 7 into which which has an outlet pipe 12. Thus thefluid on reaching products, as on heating, such fluids should be avoidedor adequate means for cleaning the permeable body at regular intervalsshould be provided. Preferably they ing the grooves 4 will flow tochamber 11 and be exst th o s th p p 1 The member} having good thermalconductivity and being surface to surface contact with the outersurface' of bearing 1 will provide for a ready transfer of heat from thebearing to itself. Being permeable, it obviously has a vast heattransfer surface perunit of volume. Further, the air which is forcedthrough the permeable member is broken down into innumerable streams,minute in magnitude, I, therefore, have the heat of thebearing-transferred to surfaces very great in .sum where it istransferred to minute streams of air. Thus it will be apparent that veryeflicient use of space and volume of fluid is achieved. The large amountof heat removed lowers the temperature of bearing 1, as well as that ofthe lubricating film in contact therewith, to values suited to saidlubricant being used. Obviously the permeability'required andjthe airflow will be adapted to securing this result.

Some heatwill also be transferred from the bearing to the supportingmember 3 (though this heat flow be comes negligible at even moderaterates of fluid flow) through the permeable member 2 and also to the airas .it flows over the surface of the bearing when it is in grooves 4enroute to chamber 7.'

It will be apparent that the strength of material required to supportthe bearing, thetemperature of the bearing without any cooling and thetemperature at which ,it is desired to maintain it, are factors whichgovern the selection of the permeable material.

In Figure 3, a bearing mounting v21 for use with a shaft subjected tohigh heat such as, for. example, the shaft of an exhaust draft fan in aboiler plant is'shoWn. A shaft 13 is surrounded by hearing shells 14 ofbronze which are secured to a pillow block 15. Inserted in cutoutportions of the pillow block are permeable metal bands 16. Longitudinalgrooves 17 are located in the facesof metal bands 16 which are adjacentthe bearing shells 14. Similar grooves 18 are cutinto the opposite 5faces of the metal bands.

-. A cooling fluid is pumped tochamber 19 and through thecircumferential grooves 20 reaches grooves 18. Since the ends of grooves18 abut against the pillow block, the fluid must pass through thepermeable bands 16 to grooves 17 whose end-s likewise abut against thepillow block. Circumferential grooves 22 and connected passages 23 and24 provide an exhaust path for the fluid from the grooves 17.

In the case of an exhaust draft fan, passage 24 may be connected to thelow pressure side of said exhaust draft fan so that the differencebetween atmospheric and suction pressures may produce the desired fluidflow.

The bearing mounting in addition has conventional packing glands 26, anoiler ring 27 and an oil chamber 28. The high heat of shaft 13 istransferred to bearing shells 14 which, in turn, transfer it readily tothe permeable bands 16. Obviously as the rate of heat removal fromhearing 14 is increased, the temperature of 13, 14, and all other partsis lowered so that at an appropriate rate of fluid flow, the desiredtemperature in bearing 14 is attained. As in the previous illustration,the heat in these bands is very efficiently transferred to the coolingfluid.

In view of the methods described, it should be obvious that the coolingof engine cylinders, for example, would be substantially shown in Figs.3 and 4 if shaft 13 is replaced with hot cylinder gases and thelubricating means are replaced and the channels thereof to the shaft areclosed. Since both the permeability and the thickness of the permeablebody may be locally modified, increased cooling may be attained readilyat exhaust valve seats, cylinder heads, and other hot spots, a resultnot readily secured by other methods of cooling. Obviously a furtheradvantage of this method of cooling is securable in the case of enginecylinders and other pressure vessels in that the permeable body may beseparated from the heat source by a shell, such as the shell 1 of Figs.1 and 2 barely thick enough to take the wear and corrosion expected andallow a small amount for the bridging of the widths of channels such asthe channels 4 of Figs. 1 and 2, with safety. Virtually the whole hoopstrength can be placed in thin Walls such as member 3 which are atsubstantially constant temperature differing little from atmosphericthroughout the length and thickness thereof.

It is not desired to be limited except as set forth in the followingclaims.

This application is a division of application Serial No. 791,200, filedDecember 12, 1947, now Patent No. 2,774,- 566 granted December 18, 1956.

What is claimed is:

1. In combination, a structural part subject to heating, a body of fluidpermeable material of good thermal conductivity abutting said structuralpart and forming with said structural part a common interface, saidpermeable body having a face opposite said interface, means to in- .6troduce a cooling fluid under pressure to said face opposite theinterface, means to exhaust the cooling fluid from the interfaceincluding passages in the interface whereby the cooling fluid flowsthrough the permeable body in the direction from the face opposite theinterface to the interface to provide a substantially uniform cooling ofthe permeable body and the structural part.

2. In combination, a structural part subject to heating, a body of fluidpermeable sintered material of good thermal conductivity abutting saidstructural part and forming with said structural part a commoninterface, said permeable body having a face opposite said interface,means to introduce a cooling fluid under pressure to said face oppositethe interface, means to exhaust the cooling fluid from the interfaceincluding passages in the interface whereby the cooling fluid flowsthrough the permeable body in the direction from the face opposite theinterface to the interface to provide a substantially uniform cooling ofthe permeable body and the structural part.

3. In combination, a structural part subject to heating, a support forsaid part formed of fluid permeable material having high compressivestrength abutting said structural part and forming with said structuralpart a common interface, said support having a face opposite saidinterface, means to introduce a cooling fluid under pressure to saidface opposite the interface, means to exhaust the cooling fluid from theinterface including passages in the interface whereby the cooling fluidflows through the support in the direction from the face opposite theinterface to the interface to provide a substantially uniform cooling ofthe support and the structural part.

4. In combination, a heated liner, an enclosing body of fluid permeablematerial of good thermal conductivity abutting said heated liner andforming with said heated liner a common interface, said permeable bodyhaving a face opposite said interface, means to introduce a coolingfluid under pressure to said face opposite the interface, means toexhaust the cooling fluid from the interface including passages in theinterface whereby the cooling fluid flows through the permeable body inthe direction from the face opposite the interface to the interface toprovide a substantially uniform cooling of the permeable body and theliner.

References Cited in the file of this patent UNITED STATES PATENTS1,285,916 Bradburn et a1. Nov. 12, 1918 1,634,768 Bonner July 5, 19272,571,868 Haller Oct. 16, 1951 2,696,410 Topanelian Dec. 7, 19542,756,115 Michel July 24, 1956

